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Santillan Hepatoma Res 2020;6:63 I http://dx.doi.org/10.20517/2394-5079.2020.60 Page 7 of 14

IMAGING FEATURES
Major features
LI-RADS major features are the primary imaging features used to categorize observations as LR-3, LR-4,
or LR-5. Major features were selected to provide high specificity for hepatocellular carcinoma and are the
only features that can be used to categorize an observation as LR-5. These major features are included in
the diagnostic table and include arterial phase hyperenhancement, nonperipheral “washout”, enhancing
“capsule”, size, and threshold growth [Figure 1].

Arterial phase hyperenhancement refers to enhancement of an observation during the arterial phase that
is greater than the background liver and results in signal intensity or attenuation that is higher than the
background liver. This feature is best assessed during the late hepatic arterial phase and is present in most
HCCs that have progressed [9,10] . A peripheral pattern to the arterial phase hyperenhancement, however, has
[11]
been associated with non-HCC malignancies such as cholangiocarcinoma and metastases [Figure 4] .
Therefore, only nonrim arterial phase hyperenhancement should be used for the assignment of LR-5
category to an observation.

The term nonperipheral “washout” refers to reduction in enhancement in whole, or in part, within an
observation from an earlier post-contrast imaging phase to a later extracellular post-contrast phase.
“Washout” (with quotation marks) refers to visual assessment of washout appearance and does not
specifically require measurement of enhancement or construction of an enhancement curve. “Washout”
in combination with arterial phase hyperenhancement is a highly specific imaging feature of HCC [12,13] .
If “washout” is present primarily along the margins of the observation, however, the imaging feature is
instead considered peripheral “washout” and is not a major feature due to its association with intrahepatic
[11]
cholangiocarcinoma . Hypointensity on the transitional or hepatobiliary phases should not be considered
“washout” since the high specificity of washout in the literature and its inclusion in LI-RADS has been
based on exams performed with ECA. If “washout” is present in an observation prior to the transitional
phase on an exam using a hepatobiliary contrast agent, “washout” can be considered present and used as a
major feature for LI-RADS categorization.

Enhancing “capsule” describes a smooth uniform border around the majority of an observation margin that
is unequivocally thicker or distinct from any fibrotic tissue present elsewhere in the liver. To be considered
a major feature, this finding must be present on the portal venous, delayed, or transitional phase of post-
contrast imaging [Figure 5]. The term “capsule” is used in place of capsule appearance, since the imaging
finding of a “capsule” can be indicative of either a true fibrous capsule or pseudocapsule on histology.
Regardless of whether a true capsule or pseudocapsule is present, however, the imaging feature of “capsule”
is present in 12%-94% of HCCs [14-17] .

The size of an observation is the largest outer edge to outer edge dimension of an observation and
should be measured on the sequence or phase where the margins of the observation are the most clear
and distinct. Due to perfusion alterations that can manifest during the arterial phase, size should not be
assessed on the arterial phase unless the observation is not visible on any other phase or sequence. Also,
due to anatomic distortion that is often present on diffusion weighted imaging (DWI), measurements
should be avoided on the DWI sequence unless the observation is not visible on another sequence. If the
observation demonstrates capsule appearance, the capsule should be included in the size measurement.
Only observations that are 10 mm or larger are eligible to be considered definitely as HCC (LR-5) in
combination with arterial phase hyperenhancement and other major features.

Threshold growth in LI-RADS v2018 refers to the size increase of an observation by greater than 50%
within six months. Threshold growth only applies to observations that are definitely masses, since perfusion